Safety device for electric motors



July 22, 1941.

E. B. TH'URSTON SAFETY DEVICE FOR ELECTRIC MOTORS Filed March 2, 1940Patented duty 22, 134i DEVICE FUR ELECTRIC MOTORS Ernest E. Thurston,Toledo, Ohio, assignor to Hangman Elevator Company, Toledo, Ohio,

a corporation of @liio hppilcation 2, 1940, Serial No. 321,929

This invention relates to s "ety device for on electric .cto :ich dc 'sethe motor start or to continue movement :ied extent w energized.ticulariy it to a device of this rngec. so that the rho-tor will stopnot only when the safety device is. operating proper- 13;, but also whsever the safety device is not in proper operative condition.

When electric motor fails to start properly or where it overloaded orfor any reason fails to continue movement at proper speed after beingeperg it is necessary to cut off the power or r avoid burning out themotor. Devices of kind have been proposed and used to some out, butthese devices have been of c aracter rich cut oii the power only whenthe crevice was proper working order, that is, to function or a wire inthe We e or any other feature of the to work, then the power to or couldcontinue whether or not the motor operated properly; i juch safetydevice does not d completeprotection since it may get out or trier atthe very time it is needed to protect the rector. It is the primarypurpose oi this invention to provides safety device for the motor ofsuch a character that the motor cannot be started and will not continueto operate Un ess the safety device is in proper working condition. Thisinsures that the safety device will operate whenever the motor isoperated and, therefore, is complete safety device.

The objects and details the invention will appear more fully thedescription proceeds.

Firms 1 a diagram of the wiring, suitable for o e form oi theii'lvention;

of wiring for a somewhat 1 edifice. ror veutic-n.

in the ed .ie invention disclosed power lines L and Swituies i3 andv itare indicated as controlll by a relay coil. H which is connected throughline to power line it and .s connc. ed by line through switches 26' andiii to line iii.

A speed, governor 25 is indicated as being driven by a pulley driven. bya belt ill from motor it. The governor is provided with a reciprocatingmember .28 whose position is determined by the speed of the governor.Member 28 move carrier 2% which supports switch 3%. One contact ofswitch to is permanently con nected through line to line ld'while theother it claims. (01. 172M288) switch is to line E5. The operation ofthe device is as follows: resuming that the parts are in position inwhich they are indicated on the drawing and it is desired to start themotor, starting switch 2! will be closed. In the form shown, the closingof the starting switch 2| temporarily closes switch 3%, that switchagain opening before switch is completely closed. While switch isclosed, coil 35 is energized by the connection from line l5 throughbranch 38 and through line 34 and switch 33 to line l6. This actionresults in closing switches 2t and 31. When once closed, coil 35 willcontinue to be energized as long as switch 33 is closed since theconnection to line l5 will continue through branch '36 and switch 31.The closing of switches 20 and 2E energizes relay coil l1 and if theconnections are all oper ative, this results in a closing of switches isand I4 and consequent energizing of the motor.

The operation of relay Il which closes switches l3 and I 4 at the sametime opens switch it and tie-energizes coil 35. Unless connectionbetween branch 34 and line l5 is reestablished within the time fixed bythe time relay 35, switch Zll will drop open and the motor will bede-energized. if the motor starts properly governor 25; will be moved soas to lift member 28 and close switch 30, thereby reestablishingconnection through lines 3! and 32 between power line l6 and branch 34.Therefore, the motor will continue to run normally until the startingswitch is opened. If the speed drops at any time below the predeter.mined speed for which the governor is set,switch will open, and afterthe predetermined inter val time relay will allow switch 2(2- to open,thereby ole-energizing the( motor. It will he readily seen that thisresult will be obtained not only if the motor fails to operate, but alsoif the operative to protect the motor whenever the motor is energized.

While a speed governor of the common ball type is illustrated in Fig. 1,it will be readily understood that a hydraulic pressure governor,friction drag governor, magnetic governor or any other suitable type ofspeed governor may be employed in place of governor 25.

While any suitable time relay may be employed an inductance relay ispreferred, since its operation more nearly approaches perfect safetythan dash pot types, for example. Where an inductance relay is employedwith alternating current power, it will be readily understood that arectifier is interposed in the lines of the relay. one way rectifier isamply sufdcient for such an inductance relay.

While for convenience there is illustrated an automatic switch 38 forinsuring the energizing of coil 35 whenever the starting switch is movedfrom open to closed position, it will be readily understood that theclosing of switches 20 and 3'5 may be accomplished manually or bydistant control through a push button located and operated in anydesired manner. When the switches 31 and 20 are ,once closed, it will bereadily understood that they will remain closed automatically duringproper operation of the apparatus regardless of how many times the motoris started and stopped, but switches 20 and 37 may be opened by anysuitable means to avoid useless energizing of coal 35 when the motor isto be shut down for any lengthy period of time.

The form of the device illustrated in Fig. 2 operates in essentially thesame manner as that disclosed in Fig. 1 except that a movement governorswitch is employed in place of the speed governor. This is particularlysuitable for use with elevators or like motors where there is greatvariation in the operative speeds of the motor.

In the particular embodiment of the invention disclosed inFig. 2, thereisa motor 40 connected by lines 4.! and "through switches 43 and 44 withpower lines 45 and 46. A relay coil 41 controlling switches 43 and 44 isconnected by a line 48 with power line 45 and is connected by a line 49through switches 50, and 52 to power line 45. The movement governorswitch comprises spaced contact members 53 which are attached in properpositions to bridge contacts. Contact 54 is shown as being connectedthrough line 55 and switch 56 to power line 46, while contact 51 isconnected permanently through line 58 to power line 46. Contact 59 isalso connected through branch 60 to line '58 and power line 45. Contact8| is connected by line 52 through switch 83 to power line 4'6. Branch54 from line 55 between contact 54 and swith 58 is connected to one endof time relay'coil 55. The lead 65 to the other end of coil 55 isconnected by branch 5! through switches 58 and $9 with power line 45,while branch '10 from line 62 is connected with one end of time relaycoil H. The other end of time relay coil H is connected through branch12 to lines 65 and 61, while it is connected by branch 13 through switch14 to power line 45. The contacts 53 are carried by a rotating devicedriven by a belt 16 or in other suitable manner from motor 40.

It is believed unnecessary to follow the operation of the wiring in Fig.2 in detail since it operates in substantially the same manner as theconnections shown in Fig. 1, except for the employment of the two timerelays 55 and 'II' wh ch are connected with the two pairs of contacts.It will be readily seen that when contacts 54 and 51 are connected byone of the bridging members 53, then relay 65 may be energized in amanner substantially analogous to the energizing at time relay coil 35in Fig. l, but that at this time contacts 59 and BI are not bridged andthat, therefore, time relay coil ll cannot be energized through thisconnection until the bridging member moves from the position in which itis shown to a position which will bridge contacts 68 and 5!. Conversely,when contacts 59 and El are bridged, contacts 54 and 51 will not beconnected.

Since both relays 55 and H must be energized in order to continue theenergization of the starting magnet operated switch 41, it will beevident that the motor operating circuit will be broken whenever member15 fails to move a half turn, in the specific arrangement disclosed,during the time for which time relays B5 and H are adjusted. It will. bereadily understood that the moving member 15 may be connected in anysuitable way with the motor and also that one or any greater number ofseparate bridging members 53 may be employed upon this moving governorswitch.

The principle of operation having been disclosed and specificembodiments described with some indication of possible variations in theoperative parts, it will be readily understood that other changes indetails may be made within the scope of the appended claims and withoutdeparting from the principle of the invention.

What I claim is:

1. In combination with an electric motor and a switch controlling theflow of power to the motor, an electrical time relay comprising means tohold the switch closed while the relay is energized and to open theswitch a. predetermined time after the relay is de-energized, anelectric circuit for energizing the relay, and means op erated by themotor to open said circuit for a. time as great as said predeterminedtime when the motor fails to move a predetermined amount within saidpredetermined time while said switch is closed.

2. In combination with an electric motor and a switch controlling theflow of power to the motor, an electrical time relay comprising means tohold the switch closed while the relay is energized and to open theswitch a predetermined time after the relay is tie-energized, anelectric circuit for energizing the relay, a. portion of said circuitbeing in parallel, a safety switch in one of the parallel lines,connections closing the safety switch when said controlling switch isopen and opening the safety switch when said controlling switch isclosed, a second safety switch in the other parallel line, and meansoperated by the motor and controlling said second safety switch to openit for a time as great as said predetermined time when the motor fallsto move a predetermined amount within said predetermined time.

3. In combination with an electric motor, a suitable power line to themotor, a normally open switch in the power line, an electric relayclosing the switch when energized, a manually operable starting switchfor energizing said relay, a safety switch '1 series with said startingswitch, an electrical time relay closing the safety switch whenenergized and opening the switch a predetermined time after it isde-energlzed, and means operated by the motor and energizing the timerelay to keepthe safety switch closed while the motor is operatingproperly.

4. In combination with an electric motor, a suitable power line to themotor, a normally open switch in the power line, an electric relayclosing the switch when energized, a manually operable starting switchfor energizing said relay,'a safety switch in series with said startingswitch, an electrical time relay closing the safety switchwhen energizedand opening the switch a predetermined time after it is de-energized, acircuit for energizing the time relay, a switch in said circuit,mechanical connections opening the circuit switch when the power lineswitch is closed and closing the by-pass switch when the power lineswitch is opened, a normally open parallel circuit for energizing thetime relay, and means for clos ing the last said circuit while the motoris oper ating up to a predetermined speed 5. In combinatiion with anelectric motor haw ing; a power line leading thereto and a switch inlapse of each period equal to said predetermined time when driven to apredetermined speed and de-energizing the coil for a period greater thansaid predetermined time when the speed drops below a predeterminedamount.

6. In combination with an electric motor, a. starting switch and asafety switch, an electrical time relay having a coil, said relayclosing said safety switch when the coil is energized and opening thesafety switch a predetermined time after the coil is de-energized, amember operated by the motor and controlling a switch in a. lineenergizing said coil when the motor is actuated to a predetermined speedand de-energizing said coil when the motor is below said predeterminedspeed, and a line in parallel with theline con-'- trolled by themovement of the motor and a switch in said parallel line closed when thestarting switch is open and opened when the starting switch is closed. I

7. In combination with an electric motor and a switch controlling theflow of power to the motor, an electrical time relay comprising means tohold the switch closed while the relay is energized and to open theswitch a predetermined time after the relay is deenerg'ized, an electriccircuit for energizing the relay, a safety switch in said circuit, agovernor controlled by the speed of the motor and maintaining the lastsaid switch closed only while the motor moves as fast as a predeterminedspeed.

8. In combination with an electric motor and a switch controlling theflow of power to the motor, an electrical time relay comprising means tohold the switch closed while the relay is energized and to open theswitch a predetermined time after the relay is de-energized, an electriccircuit for energizing the relay, two safety switches in said circuit, atime relay for each switch, each relay comprising a coil closing theswitch when energized and opening the switch a predetermined time afterde-energization, and

means operated by the motor and energizing said coils in alternationwhile the motor is moving, whereby at least one of said safety switchesopens whenever the motor fails to operate said means rapidly enough toenergize each coil within said predetermined time after it has beende-energized. v

9. Apparatus in accordance with claim 8 and in which said means operatedby the motor and energizing said coils in alternation comprises arotating member driven by said motor and closing circuits through saidcoils in alternation.

10. Apparatus in accordance with claim 8 and in which said meansoperated by the motor and energizing said coils in alternation comprisesa rotating member driven by said motor and carrying contacts bridgingstationary contacts to close circuits through said coils in alternation.

ERNEST B. THURSTON.

